It is generally known in the art to have a patty molding machine, having a hopper for holding a supply of ground meat such as ground beef, which is progressively advanced to a fill position for delivery of the ground meat into one or more mold cavities in a reciprocal mold plate. Pressure is exerted on the ground meat to fill the mold cavities. After the mold cavities are filled, the mold plate is moved to a knock-out position where the patties can be forced out of the mold cavities for further handling.
The machines manufactured by the assignee of this application have been designed to fill the mold cavity from "back to front" through a fill slot adjacent the mold plate. A typical construction of this type is shown in application Ser. No. 657,254 filed Oct. 3, 1984, now U.S. Pat. No. 4,597,134, granted July 1, 1986.
The "back-to-front" method of filling a mold cavity has been used for several reasons. The fill slot acts as a "shut-off" valve, as the mold plate move a short distance away from the fill position. This is necessary because the plunger or other mechanism used to force the ground meat into the mold cavity on its advancing stroke, tends to pull the meat back out of the mold cavity on its retracting stroke until "shut-off" is obtained. A further reason relates to the "cover area", which is the distance from the front edge of the fill slot to the point where the mold cavity and the patty formed therein emerge from the enclosing top and bottom plates of the machine. This cover area must be the length of the largest diameter patty to prevent a direct path of flow of ground meat from the fill slot through the mold cavity and out the front end of the machine. Filling the mold cavity from "back-to-front" with the fill slot toward the rear of the mold cavity results in more easily achieving the desired cover area. Additionally, filling from the back of the mold cavity produces a flow pattern of ground meat and sinew therein, to achieve a compromise "cook-out" of the patty and have the final shape approximately round.
The filling of the mold cavity from "back-to-front" has disadvantages. The material that is molded such as ground beef has relatively high viscosity, which makes it susceptible to high pressure gradients during flow. Because of this, there are resulting density variations along the flow path in the mold cavity which results in an uneven "cook-out" of a product such as a hamburger patty. Additionally, it is difficult to control the flow pattern in the mold cavity to achieve a fiber alignment which will result in a round fresh patty remaining round when cooked. This is primarily due to the flow starting along a narrow path and then widening and then again narrowing when moving from the rear to the front of a mold cavity having a circular shape. Further, the time to fill the mold cavity is high because of the relatively long flow path required to fill the mold cavity.
The invention disclosed herein comprehends filling a mold cavity from a fill slot with their center lines coincident and the use of a pair of plates functioning as valve means for controlling flow of ground meat to the mold cavity. These plates have their adjacent edges formed with teeth which intermesh in a closed position and which provide two rows of holes for passage of ground meat to the mold cavity when open. One of the plates is movable in response to a pressure differential for movement between open and closed positions. The use of a pressure responsive valve plate in various types of molding apparatus including a patty forming machine are shown in Gilcrest U.S. Pat. No. 2,456,778, Wilcox U.S. Pat. No. 3,376,608, and Holly U.S. Pat. No. 4,272,864.